If your laptop cable isn't long enough to sit the power brick on the floor, redditor agentdax5 has a great trick for keeping it on your desk: just wrap a rubber band around it.
The rubber band will keep it from slipping and sliding around, letting you put it wherever you want without fear it'll fall off the desk (and yank the rest of your cable with it). Plus, then when you take it with you, you can wrap the cables under the rubber band (if your power brick doesn't already have a built-in mechanism for this).
LPT: Tie a rubber band around your laptop power adapter. | Reddit